1. Field of the Invention
The present invention relates to a hydraulic booster system and more particularly, to a hydraulic booster system for use in a brake device for a vehicle.
2. Description of the Prior Art
There is such a conventionally known hydraulic booster system disclosed, for example, in Japanese Patent Application Laid-open No. 113549/86.
In the above prior art system, a valve piston connected to an operating member is slidably received in a booster piston which is slidable within a booster cylinder in the hydraulic booster and which is abuttable against an operation piston in a master cylinder, so that supply and release of a hydraulic pressure into and from an output hydraulic pressure chamber facing a back of the booster piston are changed over in accordance with the relative operation between the booster piston and the valve piston. Therefore, at an initial stage of operation by the operating member, the start of operation of the booster piston is liable to be delayed due to a friction at a sealing portion between the booster piston and the booster cylinder and hence, the initial operation of the operation piston in the master cylinder is not smooth.